A new class of magenta-dye forming couplers used lately in color photography is 1H-pyrazolo[1,5-b]-1,2,4-triazole couplers. Image dyes formed from these couplers have an excellent light fastness. Examples are couplers disclosed in U.S. Pat. Nos. 4,540,654; 4,621,046; 4,882,266; 5,262,542; 5,378,587; 5,451,501, JP 60-197688; and JP 03-184980. The couplers have a unique 5/5 heterocyclic ring system. It has been solely synthesized solely from a 3-ketopropionitrile (1) as shown in the following scheme:
Reaction of a 3-ketoprionitrile (1) with hydrazine gives a 3-aminopyrazole (2). A 3-aminopyrazole )(2) is then reacted with an alkyl or aryl imidate ester hydrochloride (4) to give a N-pyrazolylamidine (5). An imidate ester hydrochloride (4) can be prepared by addition of an alcohol (R′OH) and hydrochloride to an alkyl or aryl nitrile (3). A N-pyrazolylamidine (5) can be converted to a N-pyrazolylamidoxime (6) by a reaction with hydroxylamine. O-Sulfonation of a N-pyrazolylamidoxime (6) with alkyl- or aryl-sulfonyl chloride (R″SO2Cl) followed by ring closure gives a 1H-pyrazolo[1,5-b]-1,2,4-triazole (8). In this synthetic sequence 3-aminopyrazole (2) is a key intermediate for making a 1H-pyrazolo[1,5-b]-1,2,4-triazole coupler.
There are several disadvantages, however, in using 3-aminopyrazole (2) as a key intermediate for the preparation of 1H-pyrazolo[1,5-b]-1,2,4-triazole couplers.
(1) A 3-ketoprppionitrile (1) is not readily available. It is usually prepared from a commercially available precursor like a α-halo ketone by replacing halogen with cyanide. Such a replacement reaction with cyanide is difficult and has a lot of disadvantages in environment, safety, health, and cost issues.
(2) A 3-aminopyrazole (2) is known to be highly toxic. Its use as a raw material requires lots of upfront cost. It is another significant disadvantage in terms of environment, safety, health, and cost.
(3) Down-stream chemistry from 3-aminopyrazole (2) is inflexible. It has to be reacted with an imidate ester such as 4 in the next step. Most of imidate esters are so sensitive to water that they should be used in a strictly anhydrous medium. Any amount of water present causes formation of an amide that is not reactive at all in subsequent reactions. Reaction of a 3-aminopyrazole and an imidate ester gives either N-pyrazolyl-amidine or N-pyrazolyl-imidate dependent upon pH of medium. Either one of these intermediates can be transformed to N-pyazolylamidoxime in subsequent step. It is difficult, however, to get either one of the intermediates cleanly, so that it is used without isolation in the next step. The next step reaction requires free hydroxylamine that is liberated from commercially available salt form. It often requires a strong organic base such as triethylamine, 1,5-diazabicyclo[4,3,0]non-5-ene, or 1,8-diazabicyclo[5,4,0]-undec-7-ene, which is costly and causes difficulties in waste disposal. It is a disadvantage in environment, flexibility, and cost issues.
(4) The overall process described above is so complicated and dependent upon dryness of the medium that it gives a highly variable result. It is a disadvantage in terms of consistency, yield, and cost.
It is therefore desirable to develop a simplified, environmentally favorable, less toxic, and less expensive intermediate for the preparation of 1H-pyrazolo[1,5-b]-1,2,4-triazole magenta dye-forming couplers.